RELATIVE CONTRIBUTIONS OF SUBCUTANEOUS AND INTERMUSCULAR FAT TO YIELDS AND PREDICTABILITY OF RETAIL PRODUCT, FAT TRIM, AND BONE IN BEEF CARCASSES

Carcass data from one side of 610 steers born from 1988 to 1990 in Cyc le IV of the Germ Plasm Evaluation research program were analyzed to d evelop means for carcass traits and retail product percentages at two fat trim levels (.76 and .00 cm) by yield grade categories. Weights of subcutaneous (s.c.) fat and intermuscular (i.e.m.) fat were recorded separately at each trim level. Quadratic regression curves were plotte d for percentages of roast and steak meat (R&S), retail product (RP), and fat trim components relative to incremental changes in USDA yield grade. Prediction equations were developed on a randomly chosen half o f the 610 carcasses to predict weights and percentages of R&S, RP, and fat trim using carcass traits obtained at the time of USDA grading an d then tested on the remaining half of the carcasses. In addition, pre diction equations were developed using s.c. and i.e.m. fat plus carcas s traits to evaluate the contribution of each to carcass fabrication y ields. Percentage of RP, trimmed to either .76 cm or .00 cm of fat, de creased by an average of 3.5% for each full yield grade increase. Trim ming to .00 cm of fat resulted in about 5.3% less RP compared to trimm ing to .76 cm. A prediction equation for percentage of RP trimmed to . 00 cm using adjusted fat thickness, carcass weight, longissimus muscle area, and percentage of kidney knob had an R-2 value of .54. The vari ations in percentage of R&S and percentage of RP at both trim levels w ere reduced by removing s.c. fat trimmed to .76 cm; however, considera ble variation still existed. Subcutaneous fat expressed as a percentag e of the sum of i.e.m. and s.c. fat increased as yield grade increased , but the percentage of i.e.m. fat was higher than the percentage of s .c. fat for all yield grades. On the basis of partial correlation coef ficients, i.e.m. fat was approximately twice as important as s.c. fat in accounting for variations in fabrication yields.